An ink jet recording apparatus has been known, which has a recording head for discharging ink as droplets onto a recording paper to print an image. The ink jet recording apparatus is provided with at least an ink container containing ink, to supply the ink from the ink container to the recording head. In an example, the recording head is provided with at least a nozzle and an oscillation plate driven by a piezoelectric element. Making use of pressure change in the nozzle, which is caused by oscillating the oscillation plate, the ink is supplied from the ink container into the nozzle of the recording head, and the ink is discharged through an ink outlet of the nozzle.
Because the ink is a consumable material, the ink container is often formed as a cartridge that is removably attached to the ink jet recording apparatus, so the ink may be supplied conveniently. When the ink contained in the cartridge type ink container, hereinafter called the ink cartridge, is used up, the empty ink cartridge is replaced with another that is fully filled with the ink. An ink supply path is provided between an ink cartridge loading section of the recording apparatus and the recording head, so that the ink is supplied from the ink cartridge to the recording head through the ink supply path.
An ink jet recording apparatus using an ink cartridge that consists of a flexible ink bag and a case protecting the ink bag has been known, for example, from Japanese laid-open Patent Application No. 2003-300331. If the ink is exposed to air, the air will be dissolved in the ink, forming air bubbles in the ink, or some components of the ink react with oxygen, deteriorating the ink. To keep the air out of the ink, the ink cartridge uses the air-tight ink bag.
It is known in the art that the pressure inside the recording head, hereinafter called the head internal pressure, is kept negative relative to the atmosphere, in order to prevent leakage of the ink through the nozzle, which would otherwise be caused by the weight of the ink. Where the ink cartridge is placed above the recording head, the head internal pressure is so raised by the weight of the ink contained in the ink cartridge, that it cannot keep the negative value relative the atmospheric pressure without any countermeasure.
In order to block the positive pressure due to the ink weight from the nozzle, it has been suggested providing a valve mechanism for opening and closing the ink supply path between the ink cartridge and the recording head, for example, from Japanese Laid-open Patent Application No. SHO 63-147651. The valve mechanism is controlled to open the ink supply path only while the recording head is activated. According to this prior art, the positive pressure due the ink weight is blocked while the recording head is inactive, so the ink leakage from the recording head is prevented.
However, because the above prior art keeps the ink supply path open during the recording, there remain some concerns about stability of ink-discharging and ink leakage during the recording. The pressure due to the ink weight varies with consumption and thus reduction of the ink contained in the ink cartridge, whereas the head internal pressure varies with the discharged amount of ink. So the head internal pressure cannot exactly be kept negative without adjusting the amount of the ink to be supplied to the recording head in accordance with the variations in the positive pressure due to the ink weight and the variations in the head internal pressure.